1. Field of the Invention
This invention relates to a reforming process utilizing as a catalyst a composite of ZSM-5 type zeolite and a conventional reforming catalyst such as platinum-rhenium on alumina.
2. Description of the Prior Art
Catalytic reforming of naphtha feed stocks has long been known in the petroleum industry. Most naphtha feeds contain large amounts of naphthenes and paraffins and consequently have low octane numbers. By means of various hydrocarbon conversion reactions, catalytic reforming has improved the octane number of naphtha feed stocks. Some of the more important conversion reactions that take place during catalytic reforming are dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to iso-paraffins. A less desirable reaction that also occurs during reforming is the hydrocracking of long chain paraffins to gaseous hydrocarbons such as methane and ethane.
The above reforming reactions have previously been catalyzed by catalysts comprising porous supports, such as alumina, that have dehydrogenation promoting metal components impregnated or admixed with the support. Platinum on alumina and, more recently, bimetallics, such as platinum and rhenium on alumina, are examples of these catalysts.
Reforming catalysts should possess high selectivity, high activity and good stability. Selectivity in reforming is the ability of a catalyst to selectively produce high yield of high octane products, such as aromatics, from compounds that have relatively low octane numbers, such as naphthenes and paraffins. The activity of a catalyst is the ability to convert the feed stock into all products without regard to selectivity. A stable catalyst is highly desirable so that the activity and selectivity characteristics of a catalyst can be maintained during prolonged periods of operation.
It is known in the art to admix certain zeolites with other catalysts. For instance, British Pat. No. 1,056,493 discloses mixing together an alumina-supported platinum catalyst and a chabazite zeolite and using it in a hydrocracking operation. British Pat. No. 1,255,544 discloses a dual purpose catalyst comprising a zeolite, especially mordenite, having incorporated therein both platinum and rhenium. However, these patents do not suggest the catalysts of this invention since they do not afford the same advantages. The octane number improvement with the catalysts of this invention is significantly greater than can be obtained with those of the British patents mentioned.
U.S. Pat. No. 3,365,392 discloses the catalytic reforming of gasoline charge stock to produce high octane reformate and LPG by contacting a charge with a catalyst comprising a platinum group metal on a support comprising a finely divided crystalline aluminosilicate suspended in alumina matrix. The preferred aluminosilicate is the hydrogen or polyvalent form of mordenite, especially the hydrogen form thereof. A similar disclosure is found in U.S. Pat. No. 3,267,022, except that the conversion process is hydrocracking.
U.S. Pat. No. 3,546,102 is concerned with a hydrocarbon conversion catalyst consisting essentially of a co-catalyst support and a Group VIII metal. The support contains an absorbent refractory inorganic oxide and mordenite structure zeolite. The preferred metal is platinum, and it is incorporated into the zeolite-inorganic oxide blend after blending but before drying and calcining.
Other U.S. Patents disclosing catalytic composites comprising plantinum, or rhenium, or both, optionally a matrix and mordenite as the sole or preferred crystalline aluminosilicate are U.S. Pat. Nos. 3,369,997, 3,376,214, 3,376,215, 3,464,929, 3,511,773, 3,523,914, 3,544,451, 3,562,108 and 3,574,092.
With respect to the disclosures in the patents above respecting the combination of mordenite, matrix and, for example, platinum, it will be shown that such combination does not give the advantages of the composite of the present invention.
U.S. Pat. No. 3,758,402 teaches hydrocracking of hydrocarbons using catalyst composed of two zeolites and, preferably, a matrix material such as alumina. The composite may also contain a hydrogenation-dehydrogenation component such as platinum. The two zeolites are ZSM-5 and an aluminosilicate having a pore size greater than 7 A.
Finally, U.S. Pat. Nos. 3,702,886 and 3,709,979 respectively disclose and claim ZSM-5 and ZSM-11 as novel compositions of matter. The compositions, which are useful in hydrocarbon conversion reactions, especially cracking, may optionally contain a matrix and a hydrogenation-dehydrogenation component. The matrix material may be selected from clays, silica and/or metal oxides.